Dinuclear zinc(II) complexes of tetraiminodiphenol macrocycles and their interactions with carboxylate anions and amino acids. Photoluminescence, equilibria, and structure

The reaction equilibria [H4L](2+) + Zn(OAc)(2) reversible arrow [Zn(H2L)](2+) + 2HOAc (K-1) and [Zn(H2L)](2+) + Zn(OAc)(2) reversible arrow [Zn2L](2+) + 2HOAc (K-2), involving zinc acetate and the perchlorate salts of the tetraiminocliphenol macrocycles [H4L1-3] (ClO4)(2), the lateral (CH2)(n) chains of which vary between n = 2 and n = 4, have been studied by spectrophotometric and spectrofluorimetric titrations in acetonitrile. The photoluminescence behavior of the complexes [Zn2L1](ClO4)(2), [Zn2L2(H2O)(2)](ClO4)(2), [Zn2L2(mu-O2CR)](ClO4) (R = CH3, C6H5, p-CH3C6H4, p-OCH3C6H4, p-ClC6H4, p-NO2C6H4), and [Zn2L3(mu-OAc)](ClO4) have been investigated. The X-ray crystal structures of the complexes [Zn2L2(H2O)(2)]-(ClO4)(2), [Zn2L3(mu-OAc)](ClO4), and [Zn2L2(mu-OBz)(OBz)(H3O)](ClO4) have been determined. The complex [Zn2L2(mu-OBz)(OBz)(H3O)](ClO4) in which the coordinated water molecule is present as the hydronium ion (H3O+) on deprotonation gives rise to the neutral dibenzoate-bridged compound [Zn2L2(mu-OBz)2](H2O)-H-.. The equilibrium constants (K) for the reaction [Zn2L2( H2O)(2)](2+) + A(-) reversible arrow [Zn(2)L(2)A](+) + 2H(2)O (K), where A(-) = acetate, benzoate, or the carboxylate moiety of the amino acids glycine, L-alanine, L-histicline, L-valine, and L-proline, have been determined spectrofluorimetrically in aqueous solution (pH 6-7) at room temperature. The binding constants (K) evaluated for these systems vary in the range (1-8) X 10(5).